1. Field of the Invention
This invention relates to the production of plastics, which are substantially free from urethane groups and which are based on polyisocyanates, by the reaction of aliphatic or cycloaliphatic polyisocyanates with compounds which are substantially free from hydroxyl groups and urethane groups and which have isocyanate-reactive groups, to produce the corresponding isocyanate group-containing prepolymers and subsequently chain-lengthening these prepolymers with water, polyamines or hydrazines.
2. Description of the Prior Art
The reaction between carboxyl groups and isocyanate groups which is known in principle and results in amide groups has until now not been used on a large scale for the production of plastics based on polyisocyanates, apart from the production of high molecular weight thermoplastic copolyamides (see, for example K. B. Onder et al., Polym. Prep. Amer. Chem. Soc. Div. Polym. Chem., 21, (1980), 132 ff). The reason for this may be seen in the low reactivity of carboxyl groups towards isocyanate groups, which results in the finding that, during the reaction of compounds containing carboxyl groups with polyisocyanates, secondary reactions always take place which result in an undesirable swelling of the reaction mixtures. Thus, for example during the reaction of the melt of polyesters containing carboxyl groups with conventional polyisocyanates, for example toluylene diisocyanate, highly cross-linked and completely insoluble products are obtained long before the release of carbon dioxide which would theoretically be expected.
On the other hand, amide groups are more thermo-stable than urethane groups, so that it was possible to proceed from the fact that plastics which were produced using reaction components containing carboxyl groups and were based on polyisocyanates have an increased stability to temperature influences, compared to conventional polyurethanes. Thus, an object of the present invention is to provide a method of producing such polyisocyanate-based plastics which allows the production thereof in a substantially by-product-free form.
Surprisingly, this object may be achieved by the process according to the present invention which is described in more detail in the following.